1. Field of the Invention
The present invention relates generally to waveguide converters, and more particularly, to a structure of a waveguide input unit of a satellite communication/satellite broadcasting receiving outdoor converter (also referred to as "LNB" hereinafter) mounted on an outdoor antenna for receiving satellite broadcasting.
2. Description of the Background Art
In general, a waveguide inlet of a LNB is provided between a waveguide on the side of a primary feed horn of a BS antenna and a main body of the waveguide of the LNB for receiving a radio wave of a predetermined band. The waveguide on the side of the primary feed horn constitutes an output side of the BS antenna (a parabola antenna etc.), while a probe connected to a microstrip line is provided in the waveguide main body of the LNB.
FIG. 4 is a sectional view showing a structure of an inlet of a conventional LNB waveguide. In this conventional example, a probe 3 is provided so as to jut out of a hole 2 provided at an inner side surface of a hole 4 of a waveguide main body 1 into the hole 4. The probe 3 is coupled to a strip conductor (not shown) of a microstrip line 20 through a junction portion 5. Then, a radio wave in the waveguide main body 1 is transmitted through the probe 3.
With the structure of the conventional example shown in FIG. 4, however, the portion 5 at which the microstrip line 20 and the probe 3 are coupled to each other generates a signal loss. This is because the probe 3 structured of a conductor of brass etc. surrounded by resin such as Teflon, causes variations of elements in size, variations in diameter of holes of the microstrip line 20 to which the probe 3 is attached and the amount of soldering for fixing the junction portion 5, resulting in generation of a signal loss. The signal loss adversely affects a noise figure (in general, a target noise figure is on the order of 1.0 dB, which is reduced by 0.03-0.07 dB due to said signal loss). Therefore, signal loss should be often compensated for and adjusted by the strip conductor on the microstrip line 20. This increases operation loss.
In addition, the necessity of providing the hole 2 with a precise diameter size and fine-finished surface at the side of the hole 4 of the waveguide main body 1 along with the necessity of an expensive probe make the LNB waveguide inlet inapplicable to mass production and unprofitable.